Method and installation for fire extinguishing using a combination of liquid fog and a non-combustible gas

ABSTRACT

A method for fighting a fire sprays a liquid fog in a total action space (1; 21) about the fire by means of at least one spray head and sprays a non-combustible gas within a partial space (3; 3a; 23) which is within and small in relation to the volume of the total action space (1; 21). The non-combustible gas is used, in addition, as propellent gas for at least one hydraulic accumulator (10; 14; 30) for spraying of the liquid fog. The spraying of the non-combustible gas is initiated at least essentially simultaneously with the spraying of the liquid fog.

The present invention relates to a method and an installation forfighting fire, in particular for spaces involving risk for fire under afloor structure or in cabinets for electrical apparatuses, and whichcomprises at least one spray head or sprinkler for spraying a liquidfog.

Spaces in question are e.g. computer rooms with cable channels runningunder the floor and possibly communicating with different kinds ofapparatus cabinets, or ship engine rooms with objects liable to catchfire under the floor in the so-called bilge space.

A serious problem with such spaces is that cable channels, apparatuscabinets etc. are narrow in general and, in addition, have cables,frameworks, pipes etc., whereby difficultly accessible corners areformed. It is very difficult to position spray heads or sprinklers insuch a way that the liquid fog has access to all corners; anunproportionally large number of spray heads is required, resulting inan expensive installation, and because of the general narrowness theliquid fog does not come into its own but turns into large water dropswhich just run down the structures.

It is the object of the invention to provide a new method and a newinstallation for fighting fire, in order to solve the above problems.

According to the method of the invention, a liquid fog is sprayed in themajor part of the space, which major part can be considered as a normalroom, while a non-combustible gas, preferably heavier than air, issprayed into the narrow partial spaces for cables etc. The gas inquestion can preferably be argon gas, but a suitable mixture of argongas and nitrogen gas can also be contemplated, or in some cases evennitrogen gas only which is lighter than air. In principle, any gashaving some kind of extinguishing effect can be utilized.

The gas is well capable of penetrating into and filling up all narrowspaces and thereby smothering occurring fires. Because those spaces intowhich gas is sprayed are of small volume in relation to the so-callednormal room, into which a liquid fog is sprayed, it is avoided that thetotal concentration of gas rises to non-allowed high values which maypresent health hazard. If, e.g. in a telephone central office, argon incombination with a liquid fog is used, the gas is only about 5 % of thetotal volume, whereat the oxygen content in the room decreases fromabout 20 % to about 19 %, which is quite harmless.

If argon gas is used as extinguishing gas, the gas collects into a layerdown in the space, the gas thus well remaining under the floor and inapparatus cabinets and the like. If, in a room with gas at the floorlevel, a spray or jet of liquid fog is sprayed down to the floor, thegas is pushed away towards the walls and the corners of the room and ispushed upwards, in particular along the corners right up to upper cornerparts of the room whereto the liquid fog has certain difficulties toreach by itself. The liquid fog hereby also tends to push the gas intocabinets standing on the floor and into similar structures into whichthe liquid fog does not penetrate very easily. The concentration of e.g.argon gas can be chosen to about 10 % of the total volume, lowering theoxygen content from about 20 % to about 18 %, likewise quite harmless.An approximate general rule is that the concentration of argon gas, inorder to achieve extinguishing by pushing away (replacing) air oxygen,shall within the partial space in question be 40-50 % of the volume.With this as a basis, the partial space in question may well be about 30% of the total volume of the action space, whereat the hazard limitapplied for a human being, 15 % oxygen of the total volume, is clearedwith a safe margin.

Cable fires often generate PVC smoke gases which damage e.g. computerapparatuses. In e.g. computer rooms, the combination of extinguishinggas and liquid fog spray, according to the invention, which creates asuction along the ceiling of the room inwards to the liquid fog spray,has the effect that the gas pushes the smoke gases, including harmfulPVC gases, up towards the ceiling, whereafter the smoke gases are suckedinto the fog and on one hand are washed and cooled and on the other handare sprayed to floor level, so that computers and other sensitiveapparatuses at least essentially avoid damages. The liquid fog also hasa good general cooling effect.

The use of gases like halon and carbon dioxide for fire extinguishingpurposes has as such been known for a long time but it has been what canbe called a total use. Different from such a total use, the presentinvention is directed to, in relation to the total action space volumeinvolved in each case, a local and controlled concentration of gas tocertain partial spaces or partial areas, in combination with a liquidfog for the rest of the space. The use of halon will apparently ceasewithin a near future. Replacing gases are under development but are sofar unproportionally expensive. The present invention, which makes itpossible to manage with small amounts of gas, can make a use of evenexpensive gases economically worth contemplating. Already existinginstallations intended for halon can, for the part of the relevantpartial spaces involved in the present invention, be used with minormodifications only. In general there may be a need to add pressurereducing valves at suitable places, because installations according tothe invention preferably employ a higher operating pressure than whatexisting halon installations do.

Thanks to the fact that one can manage with small amounts of gas, it isfurther possible to, if so desired, use carbon dioxide in such caseswhere carbon dioxide hereto has meant a serious health hazard; thecarbon dioxide content must not exceed 5 volume % in occupied rooms.

The invention shall in the following be described in more detail, withreference to preferable exemplifying embodiments shown in the attacheddrawing.

FIGS. 1-5 show different embodiments in connection with a computer roomor similar.

FIG. 6 shows a first embodiment in connection with a ship engine room orthe like.

FIGS. 7-9 show a valve preferable for use in the embodiments of FIGS. 4and 6.

FIG. 10 shows a second embodiment in connection with a ship engine roomor the like.

FIGS. 11-14 show a preferable embodiment of a spray head mountable inthe floor of an engine room.

FIGS. 15-17 show a preferable embodiment of a gas nozzle mountable underthe floor of an engine room.

FIGS. 18-21 show a preferable embodiment of a spray head mountable atthe ceiling of an engine room.

FIGS. 22-24 show such an application of the spray head of FIGS. 11-14that preferably can be mounted in the floor of a car deck in a ship, oranother space comparable to that.

In FIGS. 1-4 the reference numeral 1 indicates a computer room the floorof which is indicated by 2. Under the floor is a cable channel 3 whichvia openings 4 and 5 in the floor communicates with apparatus cabinets 6and 7. At the ceiling of the room 1 are positioned a suitable number ofspray heads or sprinklers 8 and in the cable channel 3 are arranged anumber of gas nozzles 9.

Liquid is delivered to the spray heads 8 from one or a plurality ofhydraulic accumulators, in FIGS. 1 and 2 a liquid container 10, aso-called pressure water bottle, wherefrom the liquid is driven out bymeans of drive gas, e.g. argon, from a high pressure gas container 11.

In FIG. 1 a part of the drive gas is already from the start lead to thegas nozzles 9 via a throttle 12, in FIG. 2 delivery of gas to thenozzles 9 takes place via an e.g. electrically operated valve 13 whichcan be arranged to open when the pressure in the container 11 has fallento a predetermined value.

In FIGS. 3 and 4 the drive gas is compressed in the upper part of ahydraulic accumulator 14. In FIG. 3 drive gas is delivered to thenozzles 9 in principle in the same way as in FIG. 2 via an e.g.electrically operated valve 15, and in FIG. 4 drive gas is delivered tothe nozzles 9 by utilizing a combination of valves 16 and 17 adapted insuch a way that when the bottle 14 has been emptied of liquid and thepressure of the drive gas after expansion has fallen to apredeterminable value, the valve 16 in the liquid line to the spray head8 closes while the valve 17 in a branch line to the gas nozzles 9 opens.The embodiment of FIG. 4 has the advantage that the desired operationcan be achieved without access to electric current. A preferableembodiment of the valve 17 shall later be described in more detail withreference to FIGS. 7-9.

The embodiment of FIG. 5 works in principle in the same way as theembodiment of FIG. 1. In FIG. 5 the computer room 1 or the like has, inaddition to a cable channel 3 under the floor 2, also an upper cablechannel 3a above the ceiling of the room, with gas nozzles 9a. Gasnozzles 9b are arranged to open directly into the apparatus cabinets 6and 7. Delivery of drive gas to the nozzles 9a takes place in the sameway as to the nozzles 9 and 9b, via a throttle 12a.

In case the room 1 would not have any cable channels or similar spacesliable to catch fire under the floor but still apparatus cabinets liableto catch fire, the embodiment of FIG. 5 can be modified to settle forgas nozzles directed into the cabinets, possibly from above instead offrom below as in FIG. 5. The liquid fog sprayed down from the ceilinglevel participactes considerably in keeping the gas in the cabinets.

In FIG. 6 a ship engine room is indicated by 21, the floor of the engineroom is indicated by 22 and the bilge space under the floor is indicatedby 23. An engine, e.g. a diesel engine, is indicated by 24. At theceiling of the engine room are positioned a number of spray heads orsprinklers 25 and close to the engine 24 additionally a number of sprayheads or sprinklers 26. In the bilge space 23 are positioned a number ofgas nozzles 27.

The fire fighting installation of FIG. 6 comprises a high pressure driveunit 28 and a low pressure drive unit 29. The high pressure unit 28includes a number of liquid bottles 30, the walls of the out-goingrising tubes 31 of which preferably have a number of apertures atdifferent levels, as shown e.g. in the Finnish patent application924752, for successively mixing of drive gas into the out-going liquid,and drive gas bottles 32 which are arranged in two groups or batteriesindicated by A and B. Out-going liquid is directed to the relevant firezone, in FIG. 6 to the fire zone D, by means of a valve 33 whichpreferably is made as presented in the Finnish patent application925836.

The installation works in the following way.

To begin with, the liquid bottles 30 are emptied a first time by meansof one drive gas battery, e.g. the battery A. When the bottles 30 and 32are empty the low pressure unit 29 is switched in, to on one hand fillthe bottles 30 again with liquid and on the other hand feed liquid tothe spray heads 25 and 26, primarily for the purpose of cooling. Whenthe bottles 30 are full again they can be emptied a second time by meansof the second drive gas battery B. In this way the capacity of theliquid bottles can be doubled.

To the out-going liquid line 34 is joined a branch 35 which leads to thegas nozzles 27. In the line 35 is mounted a valve 36 of suchconstruction that it is closed at line pressures less than e.g. 20 barand more than e.g. 100 bar but is open within the pressure interval20-100 bar. The drive gas bottles 32 are hereby adapted in such a waythat they after completed emptying of the liquid bottles 30 have a gaspressure somewhat less than 100 bar; the gas of the bottles 32 aredelivered to the gas nozzles 27.

The drive unit shown in FIG. 6 can of course also well be used in suchfire fighting installations where a liquid fog only is sprayed, i.e.without gas nozzles 27 and gas line 35 with valve 36.

A preferred structure of the valve 36 is shown in FIGS. 7-9. Inside thevalve housing 36a, 36b is positioned a valve head 37 movable between afirst position in closing abutment, pushed upon by a spring 38, againstan opening in one valve housing part 36a, as shown in FIG. 9, and asecond position in closing abutment, with the spring 38 compressed,against an opening in the other valve housing part 36b, as shown in FIG.7. The spring 38 can without difficulty, as desirable in each case, beadapted e.g. in such a way that it holds the valve head 37 in theposition of FIG. 9 against a pressure up to about 20 bar and at apressure of about 100 bar yields so, thanks to the liquid pressure fallin an annular passage 39, adapted for this purpose, between the valvehead 37 and the valve housing part 36a, that the valve head takes theposition of FIG. 7. In both cases the valve 36 is closed. Within thepressure interval 20-100 bar the spring 38 yields partly only, as shownin FIG. 8, the valve being open for gas to flow to the gas nozzles 27,as earlier mentioned. The pressure fall for gas in the passage 39 isconsiderably smaller than for liquid at the same pressure. In this wayit can be avoided that high pressure liquid and liquid delivered by thelow pressure unit 29 go to the gas nozzles. As earlier mentioned, asimilar valve structure can likewise be used in the embodiment of FIG.4, the valve 17.

A second preferred embodiment for engine rooms and the like is shown inFIG. 10. The drive unit of the installation is in FIG. 10 similar to theone in FIG. 6, while the arrangement in the engine room 21 itself issomewhat different.

Sprinklers or spray heads 25 positioned at the ceiling of the engineroom can be similar to those in FIG. 6, likewise spray heads 26 near theengine 24. In the floor 22 of the engine room are, in addition, mounteda number of spray heads 40, preferably near to the engine 24. The sprayheads 40 are arranged to upon activation rise a distance above the floor22, while pushing off a cover 41, essentially as is presented in theinternational patent application PCT/FI92/00213, and in a first stageproduce a liquid fog spray or jet directed upwards and producing astrong suction out and up from the bilge space 23, and in a later stagespray a gas into the bilge space, generally applying that principlesolution which is shown in FIGS. 7-9. In order to secure a sufficientamount of gas in the bilge space 23 the spray heads 40 can becomplemented by a number of gas nozzles 42 which likewise apply thevalve solution of FIGS. 7-9. All sprinklers and spray heads as well asgas nozzles can thereby be fed by one and the same line 43 going outfrom the drive unit of the installation. The way of operation of thefloor spray heads 40, which are essential in the embodiment of FIG. 10,shall in the following be described with reference to FIGS. 11-14.

FIG. 11 shows a spray head 40 in stand-by state, FIGS. 12 and 13 showthe spray head in said first activated stage producing a liquid fog, andFIG. 14 shows said later activated stage spraying gas into the bilgespace.

The spray head 40 comprises a primary housing or holder 44 which isfirmly fastened to the floor 22 of the engine room by means of a flange45. The primary housing 44 has an inlet 43a for liquid and gas,respectively, and in its lower portion a number of liquid nozzles 46directed obliquely to the sides and a central gas nozzle 47 withorifices 48 preferably directed to the sides. The connection from theinlet 43a to the nozzles 46 and 47 is regulated by means of a valve head49 being under the action of a spring 50, in principle in the same wayas in the valve according to FIGS. 7-9.

In the upper portion of the primary housing 44 is slideably arranged asecondary housing 51 with a number of liquid spray nozzles 52 directedobliquely upwards to the sides. The connection from the inlet 43a to thespray nozzles 52 is regulated by means of a spindle 53 which a spring 54tries to push to the end position closing the connection, as shown inFIG. 11. The spring 54 is positioned in an annular space betweeen thehousing 51 and the spindle 53, which annular space, via a centralchannel formed in the spindle, communicates with the the inlet. Bydimensioning said annular space suitably, the pressure in the inlet canbe partly balanced e.g. in such a way that even a relatively weak spring54 is capable of keeping the spindle in the closed position according toFIG. 11 against a pressure of e.g. up to 100 bar.

When the installation is activated after a fire has started, liquid isdelivered to the spray head 40 with a pressure higher than 100 bar, e.g.280 bar, which state is shown in FIGS. 12 and 13. The secondary housing51 has been lifted up with a great force to upper end position against aretainer ring 55 and has thereby pushed off the cover 41. The highpressure has also driven up the spindle 53, the upper protruding end ofwhich secures that the cover does not remain lying in front of thenozzles 52 which now are in communication with the inlet 43a. Thenozzles 52 produce a forceful upward liquid fog spray or jet which inturn produces a forceful suction out and up from the bilge space viaframe apertures 56 adjacent the flange 45, said suction being indicatedby arrows 57. As an example can be mentioned that a liquid fog spray ofabout 5 liters liquid per minute sucks along up to 5000 liters of smokegases and air. The bilge space is in practice a sea of fire withremarkable flames being sucked out of the frame apertures 56. Theseflames, together with the also otherwise hot smoke gases, bring about avery powerful generation of steam in the sprayed liquid fog alreadyalmost immediately at floor level. The steam participates veryeffectively in extinguishing the fire.

At the same time the high pressure in the inlet 43a has hit the valvehead 49 down against the gas nozzle 47, so that the connetcion theretois closed while liquid can be sprayed out of the nozzles 46.

After the liquid bottles 30 have been emptied and the pressure of thedrive gas in the bottles 32 has fallen somewhat below 100 bar, the sprayhead 40 takes a position in principle according to FIG. 14. Thesecondary housing 51 is still in raised position but the spindle 53 hasbeen pressed back by the spring 54, so that the connection from theinlet 43a to the nozzles 52 again is closed. The spring 50 has liftedthe valve head 49 off the gas nozzle 47 which now communicates with theinlet 43a. Most of the gas flows out through the orifices 48 of thenozzle 47, a small part of the gas flows out through the nozzles 46.This state continues until the gas pressure has fallen so low, e.g. to20 bar, that the spring 50 presses the valve head 49 back to theposition of FIG. 11. The powerful generation of steam during the stageaccording to FIGS. 12 and 13 is in many cases alone sufficient forextinguishing a fire definitively, but a final fighting with gas isstill recommendable as a safety measure.

The same principle solution described above can well be applied also tothe complementary gas nozzles 42, FIG. 15 shows such a nozzle when thepressure is less than 20 bar, FIG. 16 shows the state of the nozzlewithin the pressure interval 20-100 bar, and FIG. 17 shows the state ofthe nozzle when the pressure is over 100 bar.

With floor spray heads and gas nozzles made according to FIGS. 11-17,and preferably with apertures in the wall of the riser tubes 31 of theliquid bottles 30, is achieved what could be called optimal utilizationof the drive gas without wasteful spending of liquid delivered by thelow pressure drive unit 29 of the installation.

With respect to the spray heads 25 and 26 positioned at the ceiling andnear the engine, the situation is different, i.e. they shall rather beopen at a pressure over 100 bar and below 20 bar but be closed withinthe pressure interval 20-100 bar. A preferred structure for this purposeis shown in FIGS. 18-21.

The spray head 25 has, mounted in a housing 60, a number of nozzles 61directed obliquely downwards and a central through flow nozzle 62. Theconnection between the inlet 43b and the nozzles 61 as well as thenozzle 62 is regulated by means of a spindle structure in twoco-operating parts 63 and 64 which both are acted upon by a spring 65and 66, respectively, supported against the nozzle 62. If the spring 65acting on the spindle part 63 is adapted to withstand a pressure of 100bar in the inlet 43b and the spring 66 acting on the spindle part 64 isadapted to overcome 20 bar only, the function will be as follows.

In stand-by state, according to FIG. 18, with the pressure in the inlet43b being almost zero, the spindle part 63 is pressed up by the spring65 into sealed abutment against the inlet opening and the spindle part64 is in turn pressed by the spring 66 against the spindle part 63 andthereby closes an axial, suitably throttled channel 67 running throughthe spindle part 63. The connections from the inlet 43b to all nozzlesare closed.

When the installation is activated, liquid with a pressure of e.g. 280bar is connected, whereat the whole spindle structure 63, 64 is drivento the bottom with the spindle part 64 in sealed abutment against theinlet of the nozzle 62, as shown in FIG. 19. The inlet 43b communicateswith the nozzles 61 but not with the nozzle 62.

When the pressure in the inlet 43b has fallen below 100 bar but isgreater than 20 bar, which is assumed to be the case in FIG. 20, thespring 65 pushes the spindle part 63 back to the position of FIG. 18 butthe spindle part 64 is still held in the position of FIG. 19. Theconnections from the inlet 43b to all nozzles are again closed.

When the pressure in the inlet 43b falls below 20 bar, which happenswhen the low pressure unit 29 of the installation is connected, thespindle part 64 rises up from the position of FIG. 20 to a "floating"intermediate position according to FIG. 21, whereat the connection fromthe inlet 43b to the nozzles 61 is still closed but the connection tothe nozzle 62 is open through the axial channel 67 of the spindle part63 and past the floating spindle part 64.

FIGS. 22-24 finally show such an application of the invention thatpreferably can be used in that kind of action spaces which do notcomprise difficultly accessible partial spaces liable for fire under thefloor but where the floor level itself generally can be assumed toconstitute a particular fire risk zone. As an example can be mentioned acar deck in a ship.

A car deck floor is indicated by 70 and a spray head mounted in thefloor is generally indicated by 71. The housing 72 of the spray head,with a number of nozzles 72 directed obliquely upwards to the sides, isarranged slideably in a holder 74 which is firmly fastened to the floor70 by means of a flange 75. The connection from an inlet 76 for liquidand gas, respectively, to the nozzles 73 and to an upper central gasnozzle 77 is regulated in the same way as in FIGS. 11-14, by means of avalve head 78 which under the action of a spring 79 is held in positionaccording to FIG. 22 closing the connection, e.g. in stand-by state witha low pressure in the inlet 76 and with a cover 80 on. The installationcan be operated in the same way as shown in FIGS. 6 and 10.

In FIG. 23 the spray head has been activated by connecting liquid underhigh pressure, which can be nearly 300 bar, whereat the housing 72 hasbeen lifted up to upper end position against a retainer ring 81 and thecover 80 has been pushed off by the gas nozzle 77 and has fallen to theside. The valve head 78 has by the liquid pressure been driven upagainst the gas nozzle 77 and closes connection thereto but has openedconnection to the nozzles 73 which produce a forceful liquid fog, in theway as earlier has been described.

In FIG. 24 the drive gas pressure has fallen to a value below e.g. 100bar, whereat the spring 79 has pushed the valve head off the position ofFIG. 23, so that most of the gas available at this stage, preferablyargon or another inert gas heavier than air, can flow out through theorifices 82 of the gas nozzle 77, preferably in essentially horizontaldirection, and form a gas layer along the floor 70, said gas layerpushing away oxygen and thus smothering the fire.

The invention can also be applied to isolated objects or objects in asmall group, e.g. a separate computer or a separate diesel engine in alarger room or hall, in such a way that the object is screened off thesurrounding area by means of liquid fog, using at least one butpreferably a plurality of spray heads or sprinklers positionedappropriately above and/or around the object, and gas is sprayed on,into or under the object. The liquid fog then acts as a kind of externalprotection while the gas acts as an internal protection.

The liquid droplets in the liquid fog can be of a size typically about10-200 microns, far different from conventional sprinkler installationswhich spray extinguishing liquid comparable to rain. Sprinklers andspray heads included in the installation are preferably constructed inaccordance to what is presented in the international patent applicationsPCT/FI92/00060 and PCT/FI92/00155. It is, however, of course alsopossible to apply the basic idea of the invention to low pressureoperation, utilizing local, controlled concentration of gas to a partialarea or a partial space of the total action space volume in each case.

I claim:
 1. Method for fighting fire, comprisingspraying a liquid fog ina total action space (1; 21) by means of at least one spray head,spraying within a partial space (3; 3a; 23) which is small in relationto the volume of the total action space (1; 21) a non-combustible gasusing the non-combustible gas, in addition, as propellent gas for atleast one hydraulic accumulator (10; 14; 30) for producing the liquidfog and initiating the spraying of the non-combustible gas at leastessentially simultaneously with the spraying of the liquid fog. 2.Method according to claim 1, wherein a non-combustible gas heavier thanair is used, in order to produce a layer of gas in the low part of theaction space.
 3. Method according to claim 2 used in an action spacewith walls and corners, further comprisingspraying a liquid fog on thegas layer in order to drive the non-combustible gas sidewardly and upalong the walls and up along the corners of the action space.
 4. Methodaccording to claim 2, wherein argon gas or a gas mixture with argon gasas a component is used as said non-combustible gas.
 5. Method forfighting fire, comprisingspraying a liquid fog in a total action space(1; 21) by means of at least one spray head, spraying within a partialspace (3; 3a; 23) which is small in relation to the volume of the totalaction space (1; 21) a non-combustible gas using the non-combustiblegas, in addition, as propellent gas for at least one hydraulicaccumulator (10; 14; 30) for producing the liquid fog and initiating thespraying of the non-combustible gas after the propellent gas pressure,in a container (11; 32) for the purpose, has fallen to a predeterminablevalue.
 6. Method according to claim 5, wherein initiating the sprayingof the non-combustible gas after the propellent gas has emptied said atleast one hydraulic accumulator (30) of liquid.
 7. Installation forfighting fire, with at least one spray head (25) for producing a liquidfog in an action space (1; 21) and with a gas driven drive unitcomprising propellent gas, wherein at least part of the propellent gasis arranged to be fed to gas nozzles (9; 27; 40) positioned within atleast one locally restricted partial space (3; 23) of the action space(1; 21) of the installation.
 8. Installation according to claim 7,wherein the drive unit comprises hydraulic accumulators (30), and thegas nozzles being arranged to be opened after the hydraulic accumulators(30) have been emptied of liquid, at a correspondingly fallen propellentgas pressure.
 9. Installation according to claim 8, wherein said atleast one spray head (25) is arranged to be closed at said fallen gaspressure and at a pressure of connection for the gas nozzles. 10.Installation according to claim 8, wherein the action space comprises afloor, and comprising at least one combined gas nozzle (47) and liquidfog spray head (40) mounted in the floor, the spray head being arrangedto produce a powerful suction from below the floor upwards, in order toproduce a powerful generation of steam in the liquid fog.
 11. Methodaccording to claim 1, wherein water is used as said liquid fog. 12.Method according to claim 5, wherein water is used as said liquid fog.